From DE 10 2006 014 756.1 a device for storing the hydraulic fluid of a hydraulic system of a transmission unit and a method for operating such a device are known. The device for storing hydraulic fluid is formed with at least one storage space delimited by a housing device and a delimiting device, and can be brought into active communication with a hydraulic system for the exchange of hydraulic fluid, and its volume can be varied between a minimum and a maximum as a function of the operating condition of the delimiting device and/or the housing device. The delimiting device and/or the housing device can be held by a holding device at least in the operating condition that corresponds to the maximum volume of the storage space against a restoring tendency of the housing device and/or the delimiting device starting from an operating condition which is different from the operating condition of the housing device and/or the delimiting device that corresponds to the minimum volume of the storage space, in the direction of their operating condition that corresponds to minimum volume of the storage space.
In this way a defined volume of hydraulic fluid, provided for the control of shift elements of a transmission unit, can be stored intermediately unpressurized in the storage space and, depending on the operating situation, can be introduced into the hydraulic system of the transmission unit at a defined pressure by acting upon the holding device to release the delimiting device and/or the housing device, by virtue of the restoring tendency of the housing device and/or the delimiting device. With this method for operating such a device in a vehicle with at least one hydraulically controlled structural group, the detent mechanism of the holding device is deactivated when there is a need to pass the hydraulic fluid out of the storage space and into the hydraulic system, in order to be able to actuate a shift element(s) as required by the operating situation by way of the hydraulic fluid volume stored intermediately in the storage space.
A disadvantage of this, however, is that during various operating situation changes of the hydraulic system, the delimiting device and/or the housing device cannot be converted to an operating condition in which the holding device or its detent mechanism is locked and the delimiting device and/or housing device are not held by the holding device during the current operating condition against the restoring tendency of the housing device and/or delimiting device, and the hydraulic fluid stored in the device, or its storage space, escapes uncontrolled from the storage space because of the restoring tendency.
Accordingly, the purpose of the present invention is to provide a method for actuating a hydraulic storage device by way of which the hydraulic storage device is brought to an operating condition in which the holding device is activated and the hydraulic storage device, starting from an operating condition different from that which corresponds to the minimum volume, can be held against the restoring tendency of the hydraulic storage device in the direction of an operating condition that corresponds to the minimum volume of the storage space.